Emergent magnetic monopole and dipole screening by free electrons in aluminum/artificial spin ice heterostructures

Abstract

In this work, we present screening of magnetic monopole and dipole by the presence of a 20 nm aluminum cover layer on square artificial spin ice systems. Our measurements were performed by magnetic force microscopy on samples with and without aluminum at remanence, after application of successive external magnetic field steps. Experimental results show that both evolution of magnetization and monopole population under external field are affected by the aluminum presence. Very good agreement between those results and excitation model simulations was found when both emergent magnetic monopole and dipole strengths decrease on the presence of the aluminum cap. We suggest that the observed strength weakening of emergent particles occurs due to its field screening by aluminum-free electrons. The screening on the presented heterostructure could be used for devices design with different magnetic monopole mobility or for selective thermodynamic activation in samples close to superparamagnetic regime.